This invention relates to a method of recovering iodine contained in waste material.
Iodine is often used as a catalyst in dehydrogenation or isomerization of organic substance and is itself very expensive. When iodine or iodine compound is used industrially as a catalyst it is financially advisable to recover it from waste. Moreover, it is well known that iodine, when absorbed into the human system, may cause various toxic symptoms, and that iodine compounds, such as methyliodide, ethyliodide, which are usually generated during various chemical reactions in the presence of iodine, are poisonous to the human body.
Therefore, at chemical plants which use iodine as a catalyst for reaction of organic substances, there exist problems which require immediate attention. The iodine should be recovered on an economical basis. Such recovery from plant waste will aid and control pollution problems.
Many suggestions relating to recovery of iodine have been published. For example, in Japanese Patent Publication Nos. 5814/1971 and 35244/1971, there are described an absorbent for recovery of radioactive iodine existing as alkyliodides. Japanese Patent Publication No. 42357/1973 describes a method for iodine recovery, wherein reaction exhaust gas mixture generated by gaseous dehydrogenation reaction of organic substances, in the presence of iodine as a catalyst, is contacted with copper oxide at high temperature to give iodinated copper oxide, and iodine is liberated from the iodinated copper oxide by oxidation using an oxidation agent. Japanese Patent Publication No. 31180/1973 describes a method for recovering iodine from gas by converting iodine contained in the gas to non-volatile iodic acid by contacting the gas with aqueous solution of nitric acid of at least 15.3 N concentration.
In each of the prior methods, however, there is a disadvantage or defect which prevents widespread useage on an industrial scale.